Thermostatically controlled heating apparatus



Dec. 10, 1957 T. H. LENNOX 2,816,202

THERMOSTATICALLY CONTROLLED HEATING APPARATUS Filed D80. 27, 1955 l NVENTOR THOMAS H. LENNOX HIS ATTORNEY United States Patent 9 THERMOSTATICALLY CONTROLLED HEATING APPARATUS Thomas H. Lennox, Redondo Beach, Calif., assignor to General Electric Company, a corporation of New York Application December 27, 1955, Serial No. 555,552

2 Claims. ((1219-20) This invention relates to thermostatically controlled heating apparatus, and has as its principal object the provision of apparatus of this type including a sheathed heating unit controlled in accordance with its internal temperature.

Another object of this invention is to provide a heating system in which pressure actuated thermostatic control means responds to thermostatic temperature sensing mean located in the interior of a sheathed heating element.

Further objects and advantages of this invention will become apparent as the following description proceeds, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Briefly stated, in accordance with one aspect of my invention I achieve the foregoing objectives by providing a thermostatically controlled heating system including a tubular sheathed heater having fluid-filled temperature sensing means therein, and thermostatic switch means connected in circuit with the heater and actuated in accordance with pressure changes in the temperature sensing means so as to control its energization.

For a better understanding of my invention, reference may be made to the accompanying drawing in which the single figure is an elevation View, partially schematic and partly in section of thermostatically controlled heating apparatus embodying my invention.

Referring to the drawing, the numeral 1 designate an outer metallic sheath of a tubular sheathed heating unit in which is positioned a resistance heating element 2 which is coiled in generally helical form and which extends concentrically Within sheath 1. Helical heating element 2 is embedded in a densely compacted mass of electrical insulating heat conducting material 3 such as magnesium oxide or any other material having suitable electrical insulating and heat conducting properties. Insulating material 3 is ordinarily loaded into sheath 1 in powdered or granular form and then compacted to a dense mass in any suitable manner, preferably by elongating and reducing the diameter of sheath 1 by swagin-g or rolling. It will be understood that other heat conducting and electrically insulating materials which may not require compacting, such as alumina or magnesia cements, may be employed.

Extending centrally through sheath 1 and within helically coiled resistance element 2 is an elongated fluidfilled temperature sensing tube having a closed end adjacent but spaced from one end of sheath 1. Because of the relatively high temperatures which may be encountered inside the heating unit, a fluid such as argon gas, may be used as the temperature sensitive fluid. Temperature sensing tube 4 extends through the other end of sheath 1 being centrally supported by means of a suitable plug or seal 6. The end of heating element 2 adjacent closed end 5 of tube 4 is electrically and mechanically connected to a terminal pin 7 spaced from closed end 5 of tube 4 and projecting from sheath 1,

2,816,202 Patented Dec. 10, 1957 being centrally supported by a plug or seal member 8. At its other end resistance heating element 2 is electrically and mechanically connected to temperature sensing tube 4, a metal sleeve 9 being employed for this purpose.

From the foregoing description it will be evident that heating element 2 may be energized by connecting terminal '7 and the projecting end of tube 4 to suitable power supply lines L1 and L2. Further, it will be seen that temperature responsive tube 4 will be heated to the temperature of the interior of the sheathed unit and that the fluid in tube 4 will expand and contract in accordance with temperature changes therein.

This expansion and contraction of the fluid in tube 4 is utilized to control the energization of resistance heating element 2 so that the temperature of the heating unit may not exceed a predetermined temperature, as determined by the setting of suitable thermostatic means connected to tube 4. In practice this permits the heating unit to be operated at a high wattage value so long as the load is relatively cool and is absorbing heat from the heating unit and also provides for the cycling of the heating unit so as to reduce the rate of heat transfer when the load being heated approaches the desired temperature.

To control the energization of resistance element 2 I utilize thermostatic switching means 10 including an outer case 11, an expansible contact actuating chamber 12, a conduit 13 interconnecting-chamber 12 and the interior of temperature sensing tube 4, and a pair of contacts 14 and 15 actuated in accordance with the expansion and contraction of chamber or bellows 12. In the present embodiment, con-tact 14 is electrically connected to bellows 12, conduit 13 and temperature responsive tube 4 so that there is a direct electrical connection between contact 14 and the end of resistance element 2 which is connected to tube 4 and contact 14. However, a conventional wire conductor may be utilized if it is desired to electrically isolate conduit 13 from tube 4. As illustrated in the drawing, if conduit 13 is to be used as an electrical conductor it is desirable that insulating sleeve 16 or the like be provided over conduit 13 and the end of tube 4 projecting from the heating unit.

Bellows 12 is opposed by a spring 17 which bears against a rectangular contact actuator 18 formed of nonconducting material and provided with slots 19 and 20 through which a contact carrying spring element 21 extends. Spring member 21 rests in oppositely disposed openings in case 11 so that it is free to snap from the position in full lines to the position shown in broken lines when force is applied thereto by contact actuator 18. Spring 17 rests on a supporting collar 22 which in turn is positioned on a cam 23 actuated by a push button 24. It will be noted that by depressing push button 24 pring collar 22 is cammed upwardly so as to apply force to spring 17 and thus shift contact actuator 18 upwardly so as to snap spring 21 over center and engage contacts 14 and 15.

To prevent overheating of the sheathed heating unit it contacts 14 and 15 should fail to open, a pair of overtemperature contacts 25 and 26 have been provided, contact 25 being carried on the lower end of a plunger 27 while contact 26 is carried on a snap action spring 28 similar to spring 21. Should contacts 14 and 15 fail to open, thus causing the heating unit to overheat, switch actuator 18 will continue to travel downwardly until it engages the upper end of plunger 27 and force spring 28 downwardly until it snaps to the over center position shown in broken lines. To permit resetting of the mechanism, a reset button or plunger 29 is provided.

Referring to the electrical circuit for the apparatus described above, it will be observed that the energizing circuit may be traced from line L1 through contacts 25 and 26, through contacts 14 and to conduit 13, through bellows 12 and finally through the tube 4, sleeve 9 and the resistance element 2 back to line L2 through terminal 7. In the drawing, the parts are shown in the off position; to energize the heating unit push button 24 is depressed so as to cause the raised portion of cam 23 to support collar 22, thus applying an upward force to spring 17 sufiicient to snap spring 21 over center thus engaging contacts 14 and 15. Resistance heating element 2 is then energized and heat is generated in the heating unit. If the tubular heating unit is employed as a surface cooking unit on an electric range for example, and if a cooking utensil or other article to be heated has not been placed on the unit, it will very quickly reach a temperature which will cause 'sufiicient expansion of the fluid in temperature sensing tube 4 to actuate contacts 14 and 15 to their open position. Thereafter, as the heating unit cools, actuator 18 will engage the bottom side of spring 21 and will again cause the contacts '14 and 15 to close. Thus, the heating unit will cycle on and-off, the off cycles being considerably longer than the "on cycles, so long as a heating load is not placed on the unit. Now if a heating load such as a cooking utensil is placed on the heating unit, 'heat will be transfer-red from the heating unit to the utensil at a rate such that -the interior of the unit is kept relatively cool and the expansion of fluid in tube 4 is not sufiicient to open contacts 14 and 15. However, as the temperature of the utensil increases the rate of heat transfer thereto will decrease and at a temperature determined by the setting of thermostat 10, the heating unit will be de-energized and will thereafter cycle at a rate sufficient to maintain a relatively narrow range of temperatures in the utensil. By providing a plurality of cams such as cams 23a and 23b various temperature ranges may be obtained, it being understood that cams 23a and 23b are actuated into engagemeutlwith collar 22 by separate push buttons.

While'the details of thermostatic switch 10 forming a part of the presently preferred embodiment of my invention have been described in some detail, it will be understood that other suitable thermostatic control switches actuated by fluid pressure may be utilized.

While I have shown and described a specific embodiment of my invention, I do not desire my invention to be limited to the particular construction shown and described, and I intend by the appended claims to cover all modifications which fall within the true spirit and scope of my invention.

What I claim is:

1. Therm'ostatioally controlled heating apparatus 'comprising an electrical resistance heater including a tubular sheath, a sinuous resistance heating element within said sheath, an elongated fluid-filled temperature sensing t-ube extending longitudinally in said sheath, said tube being closed at one end adjacent to but spaced from one end of said sheath, the end of said heating element adjacent said one end of said sheath being electrically and mechanically connected to a terminal pin spaced from the closed end of said tube and projecting from said sheath, the other end of said heating element being electrically and mechanically connected to said tube adjacent the other end of said sheath, a mass of heat conducting electrical insulating material compacted within said sheath, and thermostatic switch means connected in circuit with said heater for controlling the energization thereof, said switch means including an expansible contact actuating chamber and a conduit interconnecting said chamber and the interior of said temperature sensing tube, whereby said heater is controlled in accordance with its internal temperature.

2. Thermostatically controlled heating apparatus comprising an electrical resistance heater including a tubular sheath, a resistance heating element coiled 'in generally helical form within said sheath, an elongated fluid filled temperature sens-ing tube extending longitudinally in said sheath within said coiled heating element, said temperature sensing tube being closed at one end adjacent to but spaced from one end of said sheath, the end of said heating element adjacent said one end of said sheath being electrically and mechanically connected to a terminal pin spaced from the closed end of said tube and projecting from said sheath, the other end of said heating element being electrically and mechanically connected to said tube adjacent the other end of said sheath, a mass of heat conducting electrical insulating material compacted within said sheath, and thermostatic switch means connected in circuit with said heater for controlling the energization thereof, said switch means including an expausible compact actuating chamber, a conduit interconnecting said chamber and the interior of said temperature sensing tube, whereby said heater is controlled in accordance with its internal'temperature.

References Cited in the file of this patent UNITED STATES PATENTS 983,548 Gale Feb. 7, 1911 1,052,998 Besley Feb. 11, 1913 1,367,122 iChubb et al. Feb. 1, 1921 1,663,810 .Morse Mar. 27, 1928 2,396,183 Lightfoot Mar. 5, 1946 2,755,361 Hertan July 17, 1956 

